I hopped in the truck today to run to Lowes, and it drove just fine on the way there. Then when leaving I noticed it didn't seem to be shifting right, it didn't feel right. When it would shift down from me pressing harder on the gas it never felt like it really ever dropped a gear, and some of the time when it would go to downshift it would kinda vibrate the truck. Nothing violent or dangerous but simply a shake/vibration. Anyway, that leads me to ask what that possible could be.

 

you might look for some threads on speed sensors.